Monomorphic Vs. Polymorphic Ants</b></font>

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July 1, 1999

Q: A couple of weeks ago one of our technicians asked why in some species of ants the workers are all the same size and in other ants the workers are of many different sizes. We tried finding an answer in several different places, but could not find anything that specifically answers this question. What is the reason for this? (G.L.)

A: First, let me say that I’m very impressed that one of your service technicians is bothering to look this closely at ants and to notice that they are not all the same. Certainly there are differences among species of ants and there are differences among ants within a given species and colony. A monomorphic species is one in which all of the workers are the same size. Where the workers are of varying sizes the species is labeled polymorphic.

As ants evolved over time, colonies became larger and more complex. As a result, there were an increased number of specialized activities within the colony that needed attention. It has been suggested that this increase in size and complexity and the resulting increase in specific tasks within the colony led to the evolution and development of the worker caste. Within these worker castes, the labor is divided into different tasks. As it turns out, some ants are more sophisticated in their division of labor. Generally, ant species with monomorphic worker castes are thought to be not as highly evolved as ants with a polymorphic worker caste. In monomorphic species, a worker’s job changes as the ant ages, while in polymorphic species different tasks are assigned to different-sized workers. We should remember that our understanding of the evolutionary development of ants and the sophisticated processes which operate within ant colonies is remarkably primitive and will no doubt change as we develop a better understanding of these amazing insects.

Questions can be faxed to Jeff Tucker at 713/681-9069.